Hi
Welcome to the MedHelp forum!
If you have a tummy ache and dizziness about 4 years later then the head injury is unlikely to be the cause. It is more likely that you have food poisoning or gastroenteritis or severe acidity or GERD. It can also be severe anxiety.
Since I cannot examine you and know other related conditions you may be having, nor is a detailed history possible on net, please consult your PCP for primary examination. Take care!
Go to an ER if you are scared. Do not post on the internet - get medical help. But this happened 4 years ago so a clot in your head is unlikely. You can still go to a doctor.